1. Field of the Invention
The present invention relates to an electrophotographic developing agent. More particularly, the invention relates to an electrophotographic developing agent having excellent fusing property without filming, streaking, hot offset and wrap jamming on a developing member. The electrophotographic developing agent includes a binder resin having a high acid value and a mixture of a low melting point wax and a high melting point wax as a releasing agent.
2. Description of the Related Art
Electrophotographic image forming apparatuses currently being used include laser printers, facsimile machines, copiers, and the like. These apparatuses form an electrostatic latent image on a photoreceptor using a laser. A toner is transferred to the electrostatic latent image using a potential difference, and a resulting toner image is transferred to a printing medium such as a sheet of paper to form a desired image.
As image forming apparatuses such as electrophotographic laser beam printers (LBPs), multifunction machines, and color copiers are widely used, a high quality image is required. Unlike a mono-printer, a color laser printer expresses various colors using a toner having four basic colors (Cyan, Magenta, Yellow, Black). For example, red is represented with magenta plus yellow. Thus, toner fusing property is more important than in the mono-printer.
Further, in view of environmental issue, less paper should be used and more double-side printing is required for user's convenience. The double-side printing results in more back-side contamination due to hot offset and wrap jam of a fuser than single-side printing. Of these disadvantages, wrap jam is more serious.
Furthermore, even within the life of a toner, image problems such as streaking of the toner itself and filming may be caused by letter or image printing.
To solve these problems, two or more binder resins are mixed and kneaded. The kneading conditions such as kneading temperature, screw rpm and feed rpm is controlled to improve dispersion of a releasing agent. The equipment for melting and kneading itself is improved, or a new type of melting and kneading equipment (e.g., open roll) is used to overcome these problems.
When a low melting point wax is used as a releasing agent to improve the fusing property, hot offset and wrap jam also occur. To reduce these problems, a high melting point wax is added to the low melting wax. However, in this case, the fusing property is deteriorated and it is difficult to disperse the releasing agent in a binder resin. Thus, further improvement in the electrophotographic developing agent is required.